1. Field of the Invention
Embodiments of the present invention relate to a method for manufacturing an optical fiber that is inserted into an insertion portion of an endoscope and guides light, the optical fiber, and an endoscope including the optical fiber.
2. Description of the Related Art
Medical endoscopes need to illuminate an object in order to observe the inside of a dark body cavity. Therefore, a light guide is used to guide light generated by a light source apparatus to an illumination portion disposed in a distal end portion of an insertion portion of the respective endoscopes.
A light guide has a configuration in which numerous optical fibers are bundled. As illustrated in FIG. 1, each of the respective optical fibers 10 (with an outer diameter φF) includes a core 11 (with an outer diameter φC) that transmits light and a clad 12 that is provided on an outer circumferential portion of the core 11 and reflects light to prevent the light from leaking to the outside from a side face of the core. For the core 11, a high-refractive index glass is used, and for the clad 12, a glass with a refractive index that is lower than that of the core 11 is used.
As an example of optical fiber manufacturing methods, Japanese Patent Application Laid-Open Publication No. 1-215738 discloses a method for manufacturing an optical fiber for optical communications using a rod-in-tube method. In a rod-in-tube method, melt-spinning, what is called “fiber drawing”, is performed with a rod-like glass, which becomes a core, inserted into a tubular glass, which becomes a clad, in an inner portion of a heating furnace.
Here, optical fibers for endoscopes and optical fibers for optical communications both have a function that guides light and thus are similar to each other in their basic parts. However, while optical fibers for optical communications each convey light with a predetermined narrow range of wavelengths over a long distance of several kilometers or more, optical fibers for endoscopes need to guide a large amount of light with a broad range of wavelengths, i.e., visible light, although the optical fibers for endoscopes guide such large amount of light over only a short distance of several meters. Thus, although a structure of optical fibers for endoscopes and a method for manufacturing the same are similar in basic part to, but largely different in, e.g., manufacturing conditions from, a structure of optical fibers for optical communications and a method for manufacturing the same.